Paper industry continuously strives to improve paper and paperboard quality, increase process speeds, reduce manufacturing costs etc. Various chemicals, synthetic and naturally occurring, are used to treat pulp in order to improve, for example, retention and drainage, and to create physical properties such as wet and dry strength of the final paper product.
A retention agent is a process chemical that improves the retention of a functional chemical in a substrate. The result is that totally fewer chemicals are used to get the same effect of the functional chemical and fewer chemicals goes to waste. Typical chemicals used as retention aids are polyacrylamide (PAM), polyethyleneimine (PEI) and bentonite.
Drainage additives are materials that increase drainage rate of water from pulp slurry on a wire. Common drainage additives are cationic starch, acrylamide and poly(diallyldimethyl-ammonium chloride) (DADMAC).
Wet strength additives ensure that when paper becomes wet, it retains its strength. This is especially important in a tissue paper. Normal wet strength additives are urea-formaldehyde (UF), melamine-formaldehyde (MF) and polyamide-epichlorohydrin (PEA).
Dry strength additives are chemicals that improve paper strength of normal or not wet condition. Typical chemicals used are starch and PAM derivatives. The starch and PAM derivatives may be anionically or cationically charged. By using cationic starch or PAM, negatively charged fibers can bind with the cationic starch or PAM and thus increase interconnections between the fibers, and thus strength.
An example of strength additives, retention and drainage aids are disclosed in document WO 2007/136756. The document discloses Michael addition adducts of vinylamines, such as polyvinylamine (PVAM), with compounds having an unsaturated bond conjugated to an electron withdrawing group to be used as strength additives, retention and drainage aids in paper making processes.
There is, however, still a need for new additives having improved influence on retention, drainage and strength properties.